A plant contains a network of ducts for the transport from the roots to the shoot of water and substances dissolved therein. When a flower-stalk is cut off these ducts are opened, so that during the remaining life of the flower the water, which normally comes from the roots and which is constantly supplied to leaves and flowers so that they should not wilt, now has to be absorbed through the cut wound formed. It is of greatest importance for the keeping the quality of cut flowers, therefore, that the ducts in the stalks should be kept open as long as possible after the cutting, so as to make possible this transport of water and of substances possibly dissolved in the water. Choking up of the ducts may occur through bacteria and algae penetrating into them or through scar substances which are formed by the plants inside the ducts, or through the actual cut surface receiving a coating of microorganisms.
The impaired water absorption of cut flowers which have been placed in a container as a rule causes them to wilt much earlier than if they had been allowed to remain on the plant. Through frequency cutting off of the flower stalks and daily changing of the water, the life can be prolonged to some extent, but since such measures necessitate both care and effort, they are frequently neglected. By using a so-called preservative agent which is dissolved in the vase water it is possible, however, without too much effort to prolong the life. In this way one of the causes for the early wilting and death of the flowers is acted upon, namely the aforementioned choking up of the duct.
In cut flowers which have been cut off from the mother plant the nutrient reserve (consisting primarily of sugar) in leaves and flowers rapidly becomes exhausted, whereupon the flowers wilt. If this starvation can be prevented in that a nutrient substance, e.g. usually sugar, is supplied from the outside via the water, an appreciable prolongation of life becomes feasible. However, the possibility of a supply of sugar from the outside too will depend, of course, on being able to keep open the ducts in the stalks. Since a sugar solution is an excellent substrate also for bacterial growth, the addition of sugar to the base water entails the risk, though, that stoppage of the ducts is increased. This too can be prevented by the addition of a so-called preservative agent (bactericidal agent) to the water as a result of which the duct openings remain open and nutrient supplied to the water can be absorbed by the cut flowers.
The presence of large quantities of bacteria in vases with cut flowers has been established. A bacteria count of up to 10.sup.13 ml.sup.-1 has been reported. Attention has been drawn in particular to the occurrence of so-called gram-negative pathogens in flower vases in a hospital environment.
In order to prolong the life of cut flowers U.S. Pat. No. 4,167,832 discloses a coat or a label which contains active material for directly contacting the water so that on immersion of the label in the water a reaction is started by which at the entire surface of the coat chlorine is released from the layer. The quantity of chlorine which at any given time is present in the water is determined partly by the rate of reaction, partly by the consumption and evaporation of chlorine from the liquid surface. On application of the technique described in the patent specification it is found that when the label is immersed in the water, a very rapid liberation of chlorine is initiated which leads to a rapidly increasing chlorine concentration in the water. According to the patent specification this agrees with the effect aimed at, since it is the intention through a rapidly increased concentration of chlorine to kill quickly all bacteria in the water and prevent thereby any stopping up of the liquid and nutrient duct endings at the cut surface.
A serious disadvantage associated with release of a large quantity of chlorine into the vase water during a very short period is that the high chlorine concentration which arises in the water causes damage to cut flowers with sensitive foliage and sensitive stalks.
It is a further disadvantage that the active agent is consumed relatively quickly which in turn leads to premature dimination of the chlorine concentration of the water, that is to say the flowers wilt earlier than would be the case with a better distribution in the release time of the chlorine.
The label in accordance with the aforesaid patent has the further disadvantage that the active substance is set free when the label comes into contact with water during transport or storage. When the active substance is chlorine, a strong smell of chlorine will ensue. On skin contact with the label, skin irritations easily can occur which may cause problems for persons frequently handling the product, e.g. employees in flower shops. There is also a risk that clothes may be damaged on coming into contact.